This invention relates to an X-ray tube rotating target drive rotor and more particularly to an electric induction motor rotor in the tube on which a target anode disc is mounted for rotation.
Ordinarily an X-ray beam generating device, referred to as an X-ray tube, comprises spaced dual electrodes of an electric circuit in an evacuated chamber or tube. One of the electrodes is a thermionic emitter cathode electrode which is mounted in the tube in spaced apart relationship to a target or anode electrode. The cathode is electrically resistance heated to generate a stream of electrons directed towards the anode target. The electron stream is appropriately focussed as a thin beam of very high velocity electrons striking the target. The target utilizes a striking surface of a predetermined material (usually comprising a refractory metal) so that the kinetic energy of the striking electrons against the target material is converted into electromagnetic waves of very high frequency, i.e. X-rays, which project from the target to be appropriately collimated and focussed for penetration into an object for interior analysis or examination purposes, for example, a human medical diagnostic procedure. The high velocity beam of electrons striking the target surface generates extremely high and localized temperatures deleterious to the target material and structure. As a consequence it has become a practice to utilize a rotating disk-like target. By means of a rotating target, the electron striking region of the target is continuously changing to avoid localized heat concentration and better distribute the heating effects throughout the target structure. Target rotational speeds in excess of 10,000 RPM are not unusual.
One example of drive means employed to rotate an X-ray tube target anode comprises mounting an electric induction motor armature or rotor for coaxial rotation in a necked down section of an evacuated glass X-ray tube. The electric motor field windings closely and coaxially surround the necked down section of the tube to act on the concentric rotor in accordance with well known electric motor principles to cause rotation of the rotor. The target disc is coaxially mounted on the rotor to be exposed to the thermionic emitter cathode.
Increases in X-ray generating capabilities with resultant larger X-ray tubes and larger targets has lead to the need for a more effective electric motor drive to provide increased starting and running torque for the target.
Accordingly, it is an object of this invention to provide an improved electric induction motor rotor for electric motor drive means of rotating targets in X-ray tubes.